homemade sausage stuffer

I am working on building a sausage stuffer. I have a 5 foot section of schedule 80 6 inch cpvc, and all the fittings required. I have my water port at the one end and all of the other end complete. Now I am working on the piston. I have a friend with a lathe and I got a piece of 6 inch round nylon stock to turn down to fit the ID of the pipe. Can anyone help me in determining the clearances for the piston. How much clearance should I have for the piston, and what should the o-ring size be. The ID of the pipe is 5.8 inches. Please help. Thanks